This seems to be another "size matters" kind of discussion, where the best answer is that "it is a matter of personal preference."

Reading through the responses we have a lot of different numerical sizes mentioned based upon varying individual needs, which prompted me to think about this a little differently.

I was pleased to see mentions of backups, since we frequently get posts about people losing work through accidental deletion, equipment (card / HD) failure, loss of a portable drive, or just the lack of a backup.

Our work should be more valuable than the cost of the card, so I would suggest all of us would benefit from working out what size of card holds a little more work than we would normally do on a specific day / weekend / project or whatever, and have at least two of those.

More importantly some of us need to look at our operating style and develop some kind of process to minimize loss when (more likely than if) something goes wrong. I'm sure most of us already have personal methods in place for that.

For me it's something simple like downloading my pictures to a computer at the end of every day / shoot, and making sure that the computer is being backed up the same day if possible.

I'm other sure people will have many better suggestions.

Working out how much and what type of work we do, and then how to make sure it doesn't get lost would probably provide some of us with a decent method answer to the original size question.

Good luck.